Languages change, usually very slowly, sometimes very
rapidly.
There are many reasons a language might change. One obvious
reason is interaction with other languages. If one tribe of
people trades with another, they will pick up specific words and
phrases for trade objects, for example. If a small but
powerful
tribe subdues a larger one, we find that the language of the elite
often shows the influence of constant interaction with the
majority,
while the majority language imports vocabulary and speaking styles
from
the elite language. Often one or the other simply
disappears,
leaving behind a profoundly altered "victor." English is, in
fact, an example of this: The Norman French of the
conquerers has
long disappeared, but not before changing Anglo-Saxon into, well,
a
highly Frenchified English.

If a people are isolated on islands or mountain valleys, language
can change very slowly indeed. But it still changes.
For
example, in the highlands of Papua New Guinea are many dozens of
languages, each quite different from its neighbors. But they
are
apparently the results of long-term isolation rather than mutual
influence. The same has happened in the Caucasus Mountains
between Russia and Turkey and Iran, among the American Indians of
the Pacific coast, and so on.

The slower mechanisms of change seem to include the "battle"
between
simplicity and expressiveness. We want our languages to
communicate as much information as possible, and yet do so
economically. We want our languages rich yet concise.
How
many prepositions or cases do we need? How many are too
much? How many verb forms do we need, and how many strain
the
brain? How many suffixes, prefixes, and irregularities can
children take before they begin to simplify? What
combinations of
sounds are easily pronounced and easily understood? And so
on.

One surprising aspect of language change is the influence of
fashion
and even of individual idiosyncracies. Although the story is
apocryphal, some say that the th pronunciation of Castillian
Spanish
was due to courtiers imitating the lisp of a young king! In
my
own family, we refer to Christmas as Wikis because of one of my
children couldn't say Christmas. Imagine if we were a part
of a
tightly knit tribal village: If others thought it was as
cute as
we did, the word Christmas could morph into Wikis in one
generation! That has probably happened millions of times in
human
history.

Let's look at a real example of one very influential people:

Around 5000 bc, between the Danube river valley and the steppes
of
what
is now the Ukraine, there lived small tribes of primitive farmers
who
all
spoke the same language. They cultivated rye and oats, and
kept
pigs,
geese, and cows. They would soon become the first people on
earth
to tame the local wild horses -- an accomplishment that would make
them
a significant part of history for thousands of years to
come. And
their proximity to the culturally more advance people of Asia
Minor -
what is now Turkey - would allow them to learn the metal working
invented
there, beginning with copper.

Beginning around 3000 bc, these people would spread into Europe
and
the Russian steppes. Around 1500 bc, they would continue
into
Persia
and India, even as far as western China. Later still (in the
last
500 years), they would spread to the Americas, Australia, the
Pacific
islands,
and parts of Africa. They would take their language with
them,
although
it would gradually change into hundreds of mutually unintelligible
languages,
including English, German, French, Spanish, Russian, Persian,
Hindi and
many more.

By examining the oldest examples of modern and classical
languages
such
as Greek, Latin, and Sanskrit, linguists have been able to
reconstruct
an educated guess as to what the language of these ancient people
was
like.
They call the language Proto-Indo-European. The work
that
went into reconstructing Proto-Indo-European has led to efforts to
reconstruct other prehistorical language ancestors as well.

To show you how these linguists did this, let's start with a
simple
example: Italian, Spanish, Portuguese,
French,
and Rumanian all come from Latin, which we still have many records
of.
Words with -ct- in the middle in Latin changed in a systematic
way,
like
this:

Latin

Italian

Spanish

Portuguese

French

English

dicto

detto

dicho

dito

dit

said

lacte

latte

leche

leite

lait

milk

lecto

letto

lecho

leito

lit

bed

nocte

notte

noche

noite

nuit

night

So one "rule" could be that a "difficult" combination of letters
like -ct- change in certain ways to end up "simpler." In
most of
the descendent languages, it just became -t-; in Spanish, it
became
ch. Another example: Words that began with pl-, cl-,
or fl-
in
Latin
changed in a systematic way as well. In this case the
initial
consonant combinations "simplified" in different ways in Italian,
Spanish, and Portuguese, but remained the same in French. In
Italian, the l became an i, in Spanish they became ll (pronounced
like
y), and in Portuguese they became ch (pronounced like sh):

Latin

Italian

Spanish

Portuguese

French

English

pleno

pieno

lleno

cheio

plein

full

clave

chiave

llave

chave

clef

key

flamma

fiamma

llama

chama

flamme

flame

The relationships among the Germanic languages are often obvious,
and linguists have reconstructed what they call Proto-Germanic:

English

Dutch

German

Danish

Norwegian

Swedish

Icelandic

book

boek

buch

bog

bok

bok

bók

come

komen

kommen

komme

komme

komma

koma

drink

drinken

trinken

drikke

drikke

dricka

drekka

And among the Slavic languages, the relationships are more
obvious
still, and they have reconstructed a Proto-Slavic:

Russian

Belarus

Ukrainian

Polish

Czech

Slovak

Slovenian

Serbo-Croatian

Makedonian

Bulgarian

mat'

maci

maty

matka

matka

matka

mati

mati

majka

maika

vera

vera

vira

wiara

vira

viera

vera

vjera

vera

vjara

son

son

son

sen

sen

sen

sen

san

son

san

Over time, the linguists learned the patterns of change, and have
used them to reconstruct languages whose original versions we no
longer
have any record
of -- such as Proto-Indo-European!
They are able to use some of the oldest versions of the different
branches of the Indo-European languages as a foundation:

English

Sanskrit

Greek

Latin

Old Irish

Gothic

Lithuanian

Old Church Slavic

four

chaturtha

tettares

quattuor

cethair

fidwor

keturi

chetyre

five

pancha

pente

quinque

coic

fimf

penki

peti

mother

maatra

mater

mater

mathir

modhir

mote

mati

brother

bhrataa

phrater

fratera

brathair

brothar

brolis

bratu

These examples are nowhere near as obviously related -- but they
are,
in fact, related. The words for brother are clearer than the
others:
You can see that the first sound varies between b, bh (a breathy
b), ph
(a breathy p), and f. The first vowel varies between a and
o.
The middle consonant varies between t and th. In all but the
last
two languages, the words end in some variation of ar or er.
Notice that the examples include Sanskrit (ancestor of the
languages of
northern India), Greek, Old Irish, and Lithuanian! Gothic is
the
oldest recorded version of the Germanic languages, and Old Church
Slavic the oldest of the Slavic languages. There are, in fact,
even
more relatives, including Albanian, Armenian, the languages of
Iran,
and many languages which haven't survived.

By examining the patterns in many languages and many words,
linguists
have reconstructed the Proto-Indo-European forms of these and many
other
words:

Proto-indoeuropean

kwetwer

penkwe

mater

bhrater

For a few more examples, here are the reconstructed
Proto-Indo-European
numbers from one to ten:

oino, dwo, trei, kwetwer, penkwe, sweks, sept, oktou,
newn,
dekm.

Look vaguely familiar?

Linguists have reconstructed other "Proto" languages for other
language
families. Some, such as the Polynesian languages, are
relatively
easy, because those languages only diverged about 1000 years
ago.
Others are nearly impossible, either because of a lack of older
written
material, or because it isn't even certain that the languages are
truly
related!

Many linguists believe that it is hard to go much further than
5000
years, even with a good set of vocabularies to work with. In
fact,
many suggest that over 10,000 years, the changes that occur are so
thorough
that no clear connection can be established between two languages
that
separated that long ago. But saying something is impossible
has
never
stopped us before! Some other linguists have indeed taken
the
leap
and used certain specialized statistical tools to project back to
a
language
that (supposedly) is the ancestor not only of Proto-indoeuropean,
but
of
the language groups Afro-Asiatic (e.g. Arabic, Hebrew, and ancient
Egyptian),
Uralic (e.g. Finnish and Hungarian), Altaic (e.g. Turkish and
Mongolian),
Dravidian (the languages of southern India), Korean, Japanese, the
languages
of eastern Siberia, and Eskimo-Aleut!

They call the reconstruction Nostratic (meaning "ours"),
and
suggest that it may have existed some 15,000 to 20,000 years
ago.
Some examples of words that may have been a part of Nostratic
include küjna
(dog), p'at (foot), haku (water), and küni
(woman).
Perhaps you recognize them from words like canine (and
hound!),
pedicure
(and foot!), aqua (and water!), and gynecologist
(and queen!).

To do this, some linguists have used a different set of
techniques. Instead of looking at a vast collection of
words,
they look at a smaller collection of words that have shown a
certain
stability in languages such as the Indo-European languages.
They
then look at statistical patterns over a large number of
languages. It is techniques like this that have allowed
linguists
to suggest, for example, that most North and South American Indian
languages are part of a language group they called Amerindian --
something the older, more meticulous methods could not do, and
many
linguists still do not trust.

But wait! Why stop there? Take a look at the
reconstructed
words from Proto-Amerindian for dog, foot, water, and woman:
akuan,
pet, haku, and kuna! These look like the
Nostratic küjna, p'at, haku,
and küni, don't
they? Some linguists go way out on a
limb and
suggest
that we can actually reconstruct at least a little bit of what
they
call
Proto-World,
presumed to exist perhaps 100,000 years ago! Kujan is the
suggested
proto-world for dog; pat is foot, haku is water;
kuni is woman.
It sounds unbelievable, and that's exactly what the majority of
linguists
think it is: unbelievable. There are way too many
opportunities
for false similarities to creep in and distort the results!

Nevertheless, it is likely that, "once upon a time," there was
indeed
only one language, one with a limited vocabulary and simple rules
for
combining
words into sentences. As the need arose, the vocabulary
could
expand
by combining old words or inventing new ones, and the rules could
become
more and more detailed. At some point, long ago, the
vocabulary
and
the grammar apparently leveled off: All languages today, no
matter
how "primitive" the people, appear to be equal in their abilities
to
express
the nuances and complexities of human life.